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Print This Article Cuadernos de Investigación Geográfica ISSN 0211-6820 2017 Nº 43 (2) pp. 629-648 Geographical Research Letters eISSN 1697-9540 DOI: http://doi.org/10.18172/cig.3201 © Universidad de La Rioja REVISITING THE ANDEAN TROPICAL GLACIER BEHAVIOR DURING THE ANTARCTIC COLD REVERSAL V. JOMELLI1*, L. MARTIN2, 3, P.H. BLARD2, V. FAVIER4, 5, M. VUILLÉ6, J.L. CEBALLOS7 1Université Paris 1 Pantheon-Sorbonne, CNRS Laboratoire de Géographie Physique, 92195 Meudon, France. 2Centre de Recherches Pétrographiques et Géochimiques, CRPG, UMR 7358, CNRS, Université de Lorraine, Vandoeuvre-lès-Nancy, France. 3Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, 0316 Oslo, Norway. 4Univ. Grenoble Alpes, LGGE, F-38041 Grenoble, CNRS, France. 5IGE, F-38041 Grenoble, France. 6Department of Atmospheric and Environmental Sciences, University at Albany, Albany, New York 12222, USA. 7Institute for Hydrology, Meteorology and Environmental Studies (IDEAM), Bogota, 07603, Colombia. ABSTRACT. The sensitivity of tropical glaciers to paleoclimatic conditions that prevailed during the Antarctic cold reversal (ACR, ca. 14.5-12.9 ka) has been the subject of a wide debate. In 2014 a paper suggested that tropical glaciers responded very sensitively to the changing climate during the ACR (Jomelli et al., 2014). In this study, we reexamine the conclusions from this study by recalculating previous chronologies based on 226 10Be and 14 3He ages respectively, and using the most up-to date production rates for these cosmogenic nuclides in the Tropical Andes. 53 moraines from 25 glaciers were selected from the previous analysis provided by Jomelli et al. (2014) located in Colombia, Peru and Bolivia. We then focused on two distinct calculations. First we considered the oldest moraine and its uncertainty for every glacier representing the preserved evidence of the maximum glacier extents during the last deglaciation period, and binned the results into 5 distinct periods encompassing the Antarctic cold reversal and Younger Dryas (YD) chronozones: pre-ACR, ACR, ACR-YD, YD and post- YD respectively. Results revealed a predominance of pre-ACR and ACR ages, accounting for 60% of the glaciers. Second we counted the number of moraines per glacier according to the different groups. 21 moraines (40%) of the selected glaciers belong to the pre-ACR-ACR chronozones while 3 moraines only (5%) were dated to the YD and YD-Holocene groups. The rest was assigned mostly to the Holocene. These results suggest that moraine records are a very good proxy to document the ACR signal in the Tropical Andes. Cuadernos de Investigación Geográfica 43 (2), 2017, pp. 629-648 629 Jomelli et al. Revisando el comportamiento de los glaciares tropicales andinos durante la inversión fría Antártica RESUMEN. La sensibilidad de los glaciares tropicales a las condiciones de temperatura fría durante la Inversión Fría Antártica (ACR, por sus siglas en inglés, 14.5-12.9 miles de años AP aprox.) ha sido ampliamente discutida. En 2014, un artículo científico revelaba una respuesta de los glaciares tropicales a la tendencia climática de la ARC (Jomelli et al., 2014); sin embargo, en 2015 nuevas producciones científicas cuestionaron la relevancia de tal conclusión. A partir de las nuevas producciónes se procedió a re-examinar las conclusiones previas, recalculando los resultados basados en cronologías 226 10Be y 14 3He. Para esta revisión, se seleccionaron 53 morrenas de 25 glaciares localizados en Colombia, Perú y Bolivia, entre los analizados por Jomelli et al. (2014) y se procedió a realizar dos cálculos diferentes. En primer lugar, se tuvo en cuenta la morrena más antigua y su incertidumbre para cada glaciar, de acuerdo con cinco períodos distintos abarcando ACR y Younger Dryas (YD): pre-ACR, ACR, ACR-YD, YD y post-YD respectivamente. Los resultados revelaron el predominio de señales pre-ACR, ACR en el 60% de los casos. Posteriormente, se contaron el número de morrenas por glaciar, teniendo en cuenta los diferentes grupos. 21 morrenas (40%) de los glaciares seleccionados corresponden con las cronozonas pre-ACR y ACR mientras que solo tres morrenas (5%) fueron datadas en los grupos YD y YD-Holoceno. El resto fue asignado principalmente al Holoceno. Estos resultados sugieren que las morrenas son un proxy muy bueno para analizar la señal de ACR en los Andes Tropicales. Key words: Tropical glaciers, ACR, Younger Dryas, Cosmogenic nuclides. Palabras clave: Glaciares tropicales, ACR, Younger Dryas, nucleidos cosmogénicos. Received: 14 December 2016 Accepted: 9 February 2017 * Corresponding author: Vincent Jomelli. Université Paris 1 Pantheon-Sorbonne, CNRS Laboratoire de Géographie Physique, 92195 Meudon, France. E-mail address: vincent. [email protected] 1. Introduction Climatic-induced glacier fluctuations during the last deglaciation (18.0-11.5 ka) have been recognized at several localities in the southern hemisphere (Thompson et al., 2000; 2006; Rodbell et al., 2009). One prominent event, the Antarctic cold reversal (ACR, ca. 14.5-12.9 ka) identified as a cold period in the southern polar latitudes, was contemporaneous with the Bølling-Allerød warm period in the northern hemisphere and ended at the onset of the Younger Dryas stadial (YD, ca. 12.8-11.6 ka). This ACR cold event provoked glacier advances in different regions of the southern mid latitudes. In New Zealand, for instance Putnam et al. (2010) documented an advance of the Pukiki 630 Cuadernos de Investigación Geográfica 43 (2), 2017, pp. 629-648 The Andean Tropical glacier behavior glacier during this cold event. ACR glacier advances were also identified in Patagonia. Glaciers of the Lago Argentino basin, Southern Patagonian Icefield experienced a major glacial stillstand or re-advance at ca. 13 ka (Strelin et al., 2014). After the ACR period the large ice lobes that filled the eastern reaches of Lago Argentino retreated and separated into individual outlet glaciers. Interestingly, this recession was interrupted only by a stillstand or minor re-advance during the YD at 12.2 ka. However the impacts of the ACR cooling event on glaciers located at lower latitudes of the southern hemisphere remained unclear in particular in the tropics. Recently Jomelli et al. (2014) established the chronology of Ritacuba Negro glacier located in the northern tropics of Colombia. The data revealed that the ACR extent of the glacier was larger than during the YD. The analysis was complemented by a synthesis of different published moraine chronologies from the Tropical Andes for the last 15 ka. On the basis of a homogenized chronology of all 10Be and 3He moraine ages across the southern Tropical Andes, the authors showed that thier behavior of ACR glacier extents exceeding those of the YD was common to the northern and southern Tropical Andes. Since this publication new 10Be and 3He production rates have been published for the tropical Andes (Martin et al., 2015; Delunel et al., 2016). This could induce possible shifts in the chronologies which may question the accuracy of the conclusions published by Jomelli et al. (2014). Within the scope of this study, we evaluate the impact of these updated production rates on the conclusions of Jomelli et al. (2014). Thus the main goal of this paper is to revisit the behavior of tropical Andean glaciers during the ACR and YD events. In other words, we investigate if tropical glaciers experienced an advance during the ACR and/or during YD periods and determine when the maximum glacial extent occurred between 14.5 and 11.6 ka ago, and whether it was synchronous between the northern and southern tropical Andes. To achieve this goal our approach consisted in recalculating the homogenized chronologies in the tropical Andes published by Jomelli et al. (2014) that cover the last 15,000 years using the new regional 10Be and 3He production rates of Martin et al. (2015) and Delunel et al. (2016). 2. Data In this study we used the same database as the one compiled by Jomelli et al. (2014), i.e. late glacial cosmogenic 10Be and 3He moraine chronologies from the Tropical Andes, including data from Venezuela, Colombia, Peru, Bolivia and northern Argentina, but we restrict our dataset to the ages younger than 15 ka (Smith et al., 2005; Farber et al., 2005; Zech et al., 2007, 2009; Glasser et al., 2009; Hall et al., 2009; Licciardi et al., 2009; Rodbell et al., 2009; Smith and Rodbell, 2010; Smith et al., 2011; Jomelli et al., 2011; Bromley et al., 2009, 2011; Blard et al., 2013; Carcaillet et al., 2013) (Table 1 and Fig. 1). The selected glaciers are located in the northern and southern tropics (Kaser, 2001). In the northern tropic, we recalculated the moraine chronologies of two glaciers, Mucubaji located in Venezuela and Ritacuba Negro glacier located in the Sierra Nevada El Cocuy, Cordillera Oriental, Colombia. The Sierra Nevada has twenty summits reaching a maximum elevation of 5300 m above sea level (a.s.l.) covered by glaciers. Cuadernos de Investigación Geográfica 43 (2), 2017, pp. 629-648 631 Jomelli et al. Table 1. Description of the selected glaciers. Reference Longitude Cosmogenic Name glacier Latitude Altitude Reference (W) nuclide (m a.s.l.) Mucubaji N 8.77 70.81 3804 10Be Carcaillet et al., 2014 Ritacuba N 6.50 72.33 4209 10Be Jomelli et al., 2014 Laguna Bara S 9.65 77.36 4045 10Be Farber et al., 2005 Quenua Ragra S 10.01 77.25 4330 10Be Smith and Rodbell, 2010 Glasser et al., 2009; Jeullesh S 10.01 77.27 4290 10Be Smith and Rodbell, 2010 Glasser et al., 2009; Tuco S 10.05 77.21 4310 10Be Smith and Rodbell, 2010 Mitococha
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